N-type organic semiconductors are needed for fabricating n-channel organic field effect transistors, p-n junction diodes, and complementary organic logic circuits. However, high performance electron transport materials are still relatively rare. Therefore, development of new n-type organic semiconductors with high charge carrier mobility, improved processability, high thermal and oxidative stability remains a major challenge in the field of organic electronics.
Among the existing n-type organic semiconductors, naphthalene diimides (NDIs) and perylene diimides (PDIs) and their derivatives are of particular interest as electron-transport materials because of their high electron affinity, chemical stability, as well as their relatively large planar structures (Anthony et al., Adv. Mater. 2010, 22, (34), 3876; Zhan et al., Adv. Mater. 23, (2), 268). Recent research has also developed other new diimide compounds, such as benzene and anthracene diimides (Zheng et al., J. Am. Chem. Soc. 2008, 130, 14410; Wang et al., J. Am. Chem. Soc. 2007, 129, 13362). Other attempts have also aimed to increase the molecular size in order to extend the π-conjugation and promote better solid state packing by expansion of the NDI and PDI cores (Gao et al., J. Am. Chem. Soc. 2010, 132, 3697; Tan et al., J. Mater. Chem., 2011, 21, (44), 18042). Beside the interesting properties obtained from thin films of arylene diimides, self-assembly of nanowires of naphthalene diimides and perylene diimides and their applications in organic nanoelectronics have also been extensively investigated, showing that a dramatic increase in electron mobility can result from crystalline nanostructures (Kim et al., Chem. Mater. 2011, 23, 682; Briseno et al., Nano Lett. 2007, 7, 2847). Another family of n-type organic semiconductors which has drawn attention is the imine nitrogen-containing heteroaromatics, including pyridine, quinoline, pyrazine, thiazole, benzothiadiazole, benzobisthiazole, etc. Members of this later class are also known for their low lying LUMO energy levels, high electron affinities and high field-effect mobilities (Tonzola et al., J. Am. Chem. Soc. 2003, 125, 13548).
Further, polymer-based semiconductors have also been studied in Babel et al., J. Am. Chem. Soc., 2003, 125, 13656; Briseno et al., Chem. Mater. 2008, 20, 4712; Chen et al., J. Am. Chem. Soc. 2009, 131, 8; Yan et al., Nature 2009, 457, (7230), 679; Huttner et al., Appl. Phys. Lett. 2008, 92, 093302; Letizia et al., J. Am. Chem. Soc. 2008, 130, (30), 9679; Zhan et al., J. Am. Chem. Soc. 2007, 129, 7246; and Ahmed et al., Chem. Mater. 2011, 23, (20), 4563.
Thus, a need exists for novel organic semiconductors, including n-type small molecule-based and polymer-based semiconductors suitable for uses as active components in organic electronic and optoelectronic devices. In particular, materials which provide good transistor performance such as high charge mobility, high on/off current ratios, and low threshold voltages are needed. Good solubility and thermal stability is also needed.